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Glossary

Terms used in accessibility research and practice. Each entry has a definition, common aliases, and category tags.

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Pareto Principle(also: 80/20 Rule, Law of the Vital Few)
The empirical observation, named after economist Vilfredo Pareto, that in many systems roughly 80% of effects come from 20% of causes. In crowdsourcing and volunteer communities, the principle predicts that a small number of top contributors produce the majority of output, while…
Pointwise Mutual Information(also: PMI)
A statistical measure used in natural language processing to quantify the strength of association between two words based on how much more frequently they co-occur in a corpus than would be expected by chance. PMI is calculated as the logarithm of the ratio of the observed…
Probabilistic Sampling(also: Random Sampling, Statistical Sampling)
A sampling method in which every member of a population has a known, non-zero probability of being selected for the sample. In accessibility evaluation, probabilistic sampling of web pages allows auditors to make statistically valid generalisations about the overall…
Psychometric validation(also: Psychometric evaluation, Instrument validation)
The process of establishing that a measurement instrument (such as a questionnaire or scale) possesses adequate reliability (consistency of measurement), criterion validity (correlation with established measures), and construct validity (measuring the intended theoretical…

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